Packing

ABSTRACT

An annular packing (30) has a cross-section in the form of a dumbbell including two enlargements (31, 32) connected by a neck (33). In a preferred embodiment the enlargements exhibit a polygonal cross-section. The packing advantageously replaces an O-ring seal in which the interior diameter of the ring is large relative to the diameter of the cross-section of the ring. The packing is arranged between two parts driven at different speeds, in precision mechanisms or in horology.

The present invention relates to a packing.

Packings are widely employed in mechanisms when it is a matter ofsealing off an apparatus from dust or water for example. In precisionmechanisms or micromechanisms, such packings are currently called 0-ringseals or indeed toroidal seals in view of their annular form and theirgenerally round cross-section.

BACKGROUND OF THE INVENTION

An example drawn from horology will make readily understandable to whatend the object of the present invention may be employed, such objectbeing readily usable in many other known domains as for instance that ofphotography (zoom lenses) or equipment in general.

In its first embodiment the invention described in patent documentCH-A-432 388 has as object a watch case comprising two elements whichmay be oriented in any desired manner relative to one another, onecomprising a first annular element bearing a glass and the other asecond annular element on which the first is rotatively mounted, apacking being inserted between these two elements.

FIG. 1 of the present invention shows such prior art, somewhat modifiedrelative to the cited document, but however remaining equivalent as faras concerns the form and arrangement of the packing.

The cross-section of FIG. 1 shows that the watch case includes acaseband 8, a back cover 13, a movement 7 housed in the case and a dial6 surmounting movement 7. An assembly 3 including a bezel 1 exhibitingan annular interior shoulder 20, a crystal 2 fitted to the bezel bymeans of a first packing 4 and an annular element forming a flange 5,may be driven in rotation relative to the caseband and to the dial.

Between the bezel and the caseband is squeezed a second round packing 9which assures sealing of the case. Packing 9 is arranged between twocoaxial cylindrical surfaces, one 22 of which bounds a portion of thebezel and the other 23 a portion of the caseband. A casing ring 10-11arranged within caseband 8 presents an annular collar 21 resting on theshoulder 20 of the bezel I so as to engage or retain the rotatableassembly 3 on caseband 8. The caseband 8 shows in its lower portion acollar 24 extending towards the center of the case. On this collar 24bears the casing ring 10-11. Screws 31 vertically positioned andtraversing bores 25 provided in collar 24 are screwed into threads 26provided in the ring in order to fix the ring to the caseband.

As mentioned hereinabove, packing 9 exhibits a round cross-section. Fromits manufacturing process, it also exhibits two diametrically opposedinjection burrs symbolized on the figure by two dashes 14 and 15. In thedimensions used here, experience has shown when the bezel 1 is rotated,packing 9 rolls or twists on itself in an irregular manner so that theburrs 14 and 15 form helices over the entire periphery of the packing,thus creating a track between the outer world and the interior of thecase, this route being used by water in order to penetrate the mechanismwithin the case.

It has been determined that the phenomenon of twisting may disappear ifthere be adopted for the O-ring a relationship between the interiordiameter Di of the ring and the diameter Dt of the cross-section of thethread constituting the ring, which is less than a limit value which maybe estimated at 20. Thus, for an O-ring currently employed inmicromechanics and which shows a diameter Di comprised between 0.8 and 5mm and a diameter Dt comprised between 0.4 and 0.5 mm, such relationshipis at worst 5/0.4=12.5 and this O-ring will not twist. On the otherhand, in the example shown on FIG. 1, O-ring 9 has an interior diameterDi of 38 mm and a cross-section Dt of 0.7 mm hence a relationshipDi/Dt=38/0.7=57.3 highly unfavourable.

In this latter case, since the diameter Di of 38 mm is imposed by thedesign, it would be necessary to provide a thread cross-section of atleast 1.9 mm to arrive at a relationship of 20 and avoid twisting of thepacking. However, such arrangement will have as consequence an increasein the overall diameter of the timepiece.

The toroidal packing 9 shown on FIG. 1 additionally shows a seconddrawback. Effectively, through the slot referenced 19 on the figure,there may be introduced not only water, but also dust which by itsabrasive action may damage the packing. The packing then runs the riskof no longer sealing out water. To provide a solution to this problem,certain designers provide two toroidal packings, one on top of theother, the first retaining dust and the second--which remainsintact--retaining water. However, here the solution is both difficultand cumbersome.

The packing ring described in patent document FR-A-1 185 726 exhibits apolygonal cross-section having two regions separated by a depressionwhich may recall a dumbbell configuration. However, the axis of suchdumbbell is shown perpendicular to the axis of the ring in a manner suchthat if this latter is employed to seal a rotating bezel, one would endup with a prohibitive increase in the overall diameter of the timepiece. On the other hand, mounted between the caseband 8 and bezel 1 of FIG.1, such ring would urge annular collar 21 onto shoulder 20 with a forcesuch that the bezel could no longer be driven in rotation except at theprice of a very substantial force not to mention the risk of seizing up.

SUMMARY OF THE INVENTION

Thus, in order to overcome the cited drawbacks, the present inventionproposes a packing which, on the one hand, does not twist up and on theother hand, replaces two superposed seals. For this, such packing ischaracterized through the fact that its cross-section shows the form ofdumbbell including two enlargements connected by a neck, the axis of thedumbbell passing through the neck and the two enlargements beingparallel to the axis of the annular packing.

The invention will now be explained with the help of the description tofollow given by way of example and referring to the drawings whichillustrate it.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-section through a case for a timepiece showing apacking according to the prior art, said figure having been discussedhereinabove;

FIG. 2 is a view similar to that of FIG. 1 in which a packing accordingto a first embodiment of the invention is shown;

FIG. 3 is a partial view and to an enlarged scale of the cross-sectionshown on FIG. 2 in which a packing according to a second embodiment ofthe invention is shown, and

FIG. 4 shows a method of manufacture of the packing shown on FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 2 takes up in part what has been shown on FIG. 1, the same partsbearing thus the same references. In place of packing 9 of FIG. 1, onFIG. 2 there will be found a packing 30 the cross-section of which showsthe form of a dumbbell defined by two enlargements 31 and 32 connectedby a neck 33. Herein is concerned a definition according to the mostgeneral meaning of the invention.

More specifically and according to a first embodiment of the invention,FIG. 2 shows that the enlargements exhibit a rounded cross-sectionrecalling to some extent the two O-ring packings brought into questionhereinabove. Packing 30 is assembled between two circular elements,bezel 1 and caseband 8 which are fitted into one another, bezel 1 beingadapted to be rotatively displaced relative to caseband 8. This assemblydefines localized pressure zones on enlargements 31 and 32, such zoneshere being four in number, namely zones 34 and 34' for enlargement 31and zones 35 and 35' for enlargement 32. During moulding of packing 30 ,it is arranged so that the injection burrs 36 and 37 are situatedoutside the pressure zones in a manner such that such zones areperfectly smooth, the burrs in certain cases being capable of creating apath for water. Thus packing 30 fulfills well the role expected of it,namely the impossibility of twisting and the faculty of retaining dustby the first enlargement 32 and water by the second enlargement 31.

FIG. 3 shows a second preferred embodiment of the invention. Here, theenlargements 31 and 32 show a polygonal cross-section. In the samemanner as in FIG. 2, such enlargements are connected by a neck 33. Herethere are found the same pressure zones 34, 34', 35 and 35'. Here,likewise, during moulding of packing 30, it will be arranged so thatinjection burrs 36 and 37 are situated outside the pressure zones. Thechoice of the polygonal form of enlargements 31 and 32 is dictated bythe concern of separating as far as possible the pressure zones from theinjection burrs. This separation is favoured by a special method ofmanufacture of the packing as will now be seen.

FIG. 4 enables explaining the method of manufacture of packing 30 shownon FIG. 3. FIG. 4 is a perspective view showing a partially cut-awaymould from which emerges the packing which is to be obtained. The mouldis formed from an upper portion 40 and a lower portion 41. When suchportions are joined, an annular cavity 42 will be formed, thecross-section of which has the form of a dumbbell including twoenlargements 31 and 32 exhibiting a polygonal cross-section, suchenlargements being connected by a neck 33. It is interesting to notethat the axis X of the dumbbell is sloped in the manner of the rim of adinner plate.

When the two portions 40 and 41 of the mould are assembled, there areformed what are called two parting surfaces 43 and 44 through whichinjection of elastic material takes place. Once such material has beeninjected (it generally concerns a polymerizable product) the twoportions of the mould are separated and the packing 30 is removed.Finally, the packing is separated from the residue of injection materialby cutting off. Such cut off, however, allows subsistence of theinjection burrs as mentioned hereinabove and which it is desirable tomaintain as far as possible away from the zones in which pressure isexerted on the enlargements when the packing is assembled on the objectwhich it is intended to seal.

In the special case of FIG. 4, the inclination X of the annular cavity42 relative to the direction Y of separation of the moulds is on theorder of 45°. In the same manner, the polygonal cross-section of theenlargements of the cavity show lines 45, 46, 47, 48, 49, 50 and 51which are oriented so as to permit separation without straining and thuswithout damaging the elastic material from which the packing is madewhen lifting of the mould takes place. If such inclination did not existand if the packing were moulded in the position which it exhibits whenit is assembled on the object to be sealed, the material would be tornaway during lifting and the joint would be unfit for use. In the samemanner, such inclination enables transferring the injection burrsoutside the pressure zones.

The fact that the packing is inclined to the exit from the moulding doesnot in any manner hinder its straight use in the part to be sealed, thiscoming above all from the fact that there exists a certain naturalstraightening and that the internal diameter Di is large relative to thecross-section Dt.

It will be mentioned that the moulding technique which has just beendescribed may be applied just as well to the packing with roundedenlargements according to figure 2. There, however, the injection burrsare closer to the pressure zones.

In the example of utilization of the packing according to the invention,hereinabove has been mentioned a timepiece. The invention is not limitedto this domain of application, but may be employed whenever one is inthe presence of two parts, the speeds of displacement of which aredifferent, such parts being assembled concentrically or telescopically.

What I claim is:
 1. An annular packing for preventing leakage of fluidand dust past two annular members having mating cylindrical surfacesseparated by a distance,said annular packing defining a central axis andbeing capable of assuming a free state and an operative state, saidoperative state being assumed when said packing is in place between saidmating surfaces, said packing having a cross-section in a planecontaining said central axis, which comprises a neck portion and twoenlargements connected together by said neck portion, said cross-sectionbeing symmetrical with respect to a straight line which is inclined tosaid central axis in said free state of said packing and which issubstantially parallel to said axis in the operative state of saidpacking, said neck portion being smaller than said distance and saidenlargements being larger than said distance wherein, in said operativestate, each of said enlargements defines annular contact faces incontact with both of said mating surfaces and said neck portion ismaintained substantially remote from said mating surfaces.
 2. A packingas set forth in claim 1 wherein said enlargements exhibit a roundedcross-section.
 3. A packing as set forth in claim 1 wherein saidenlargements exhibit a polygonal cross-section.
 4. A packaging surfaceas set forth in claim 1 wherein said mating surfaces are adapted to bedisplaced relative to another.